1. Field of the Invention
The present invention relates to a biaxially textured metal layer deposited by electroplating process on the surface of a single-crystalline or quasi-single-crystalline metal substrate, and a method for manufacturing the biaxially textured metal layer. More particularly, the present invention relates to a biaxially textured pure metal or alloy layer deposited by electroplating process on the surface of a pure metal or alloy substrate having single-crystalline or quasi-single-crystalline orientation, and a method for manufacturing the biaxially textured pure metal or alloy layer in which the surface of the pure metal or alloy layer is used as a cathode.
2. Description of the Related Art
Most of presently used materials are in the form of polycrystals. A large amount of polycrystalline materials have some crystallographic orientations.
FIG. 1 schematically shows the microstructures of the materials with various types of grain alignments. Specifically, FIG. 1(a) shows a material having randomly oriented crystal grains in any direction. FIG. 1(b) shows a material in which the crystal grains are well oriented in the direction perpendicular to the plane of a substrate but are randomly oriented in the direction parallel to the plane of the substrate. This material texture herein refers to “uniaxial texture”.
On the other hand, FIG. 1(c) shows a polycrystalline material in which the crystal grains are well aligned in the directions perpendicular and parallel to the plane of the substrate. Such texture of the metal material herein refers to “biaxial texture”. The biaxially textured material is featured by the crystallographic orientation similar to that of single crystals, as shown in FIG. 1(d).
Since the texture of materials influence the mechanical and electrical properties, many trials to control the orientation of the grains constituting the material have been performed. For example, magnetization largely depends on the orientation of crystal grains, e.g., a Fe-based metal is likely to be magnetized in the <100> direction.
Thus, {110}<100> or {100}<100>-oriented silicon steels are suitable for magnetic cores of electric devices such as transformers, motors, etc. In particular, magnetic loss and magnetic permeability of electrical steel can be improved by enhancing grain alignments. Accordingly, studies on the improvement of texture for reducing the weight of electric power devices and coil current are actively in progress.
In addition, in the case of YBCO-based high temperature superconducting wires, current transport properties largely depend on the orientation of superconducting grains. Accordingly, in order to manufacture superconducting wires having a high critical current density (Jc), superconducting crystal grains must be biaxially aligned within a few degrees.
As shown in FIG. 2, trials to impart a biaxial orientation to crystal grains of superconductors using a highly {100}<100>-oriented metal substrate have proved to be quite successful.
ORNL (Oak Ridge National Lab.) of the USA developed a so-called RaBiTS (Rolling-assisted Biaxially Textured Substrate) process, which is currently used to manufacture biaxially oriented metallic substrates required for fabricating superconducting wires.
Specifically, the RaBiTS process is used to manufacture biaxially oriented substrates for YBCO superconducting wires through rolling of a base metal and subsequent annealing.
In addition, in the case of grain-oriented electrical steel used as magnetic cores of electrical devices such as transformers, motors, etc., rolling and post-heating processes are used to induce highly oriented texture.
The rolling/post-heating process has an advantage that uniform and biaxially oriented substrates can be mass-produced.
However, the process requires large-scale facilities to carry out the rolling and post-annealing process, and it is not easy to manufacture thin and biaxially oriented metal substrates having a thickness of 100 μm or less. The difficulty is due to various problems associated with the rolling, such as cracks, nonuniform thickness, etc.
In particular, in order to use superconducting wires in large-scale power electric devices such as motors, magnets, etc., the superconducting wires must have high engineering critical current density (Je). Accordingly, thin metal substrates are advantageous because a part of the substrates do not participate in the electric power transmission.
In addition, in the case of grain-oriented electrical steel used as magnetic cores of electric devices such as transformers, etc., since eddy current loss due to the alternating current is proportional to the square of the thickness of the steel plates, thin and uniform plates are desired in terms of high efficiency.
On the other hand, grain-oriented metal plates can be realized by electroplating process, in addition to the rolling/post-annealing process discussed above. When the electroplating process is employed to manufacture a metal substrate for superconducting wires, a biaxially oriented substrate can be manufactured in a simple manner with low operating costs, compared to conventional processes using the rolling and high temperature heat treatment.
However, it is known that most of metal layers deposited by the electroplating process have high orientation on the c-axis, but no orientation on the a- or b-axis. Since only uniaxial texture can be induced by the conventional electroplating process, and thus metal layers formed by the electroplating process have fiber texture.
The present inventors reported in Korean Patent No. 352976 and U.S. Pat. No. 6,346,181 that when an external magnetic field is applied during electroplating, biaxial orientation can be induced.
These patents meet the novelty condition of patentability in which a biaxially oriented layer can be manufactured by appropriately arranging the position of electrodes and a magnetic field source. However, the biaxially oriented layer has a disadvantage of low degree of biaxial texture (Δ ω ˜7°, Δ Φ ˜21), compared to conventional processes using the rolling/post-heating (Δ ω ˜7°, Δ Φ ˜8°),.
In contrast, a biaxially textured pure metal or alloy layer manufactured using a single-crystalline or quasi-single-crystalline metal substrate, in accordance with the present invention has larger degree of biaxial orientation (Δ ω ˜4°, Δ Φ ˜5.2°) than conventional metal layers manufactured using the rolling/post-heating as well as the electroplating process.
Accordingly, since the present invention provides a metal layer having higher degree of biaxial texture than conventional metal layers manufactured using the rolling/post-annealing as well as the electroplating process, it may pave the way for future industrial applications of magnetic materials and superconductors.